A type of core-making machine that has been used for many years for making transformer cores is the belt nester. Typically, a belt nester comprises a rotatable arbor about which sections of magnetic strip steel of controlled length are wrapped in superposed relationship as the arbor is rotated, thereby building up a core form that increases in diameter as additional strips are wrapped about those previously wrapped. Wrapping of the strips is effected by use of a flexible belt that encircles the arbor and is driven to cause rotation of the arbor and any strips previously wrapped about the arbor. Strips are fed into the belt nester in such a manner that they enter between the arbor and the encircling belt; and as the belt and arbor move together, each entering strip, or group of strips, is forced by the belt to tightly encircle the arbor or any core form already built up upon the arbor. An example of a belt nester of this type is disclosed in U.S. Pat. No. 3,049,793--Cooper.
Belt nesters of the above type have heretofore been used for making cores that comprise strips of amorphous steel that are wrapped about the rotating arbor. Because the amorphous strips are very thin (e.g., typically only about 1 mil in thickness), it is highly desirable to feed them into the belt nester in stacks, each comprising a large number of the strips. Each of these stacks is preferably a packet comprising a plurality of groups of strips, each group comprising many strips stacked in superposed relationship, the groups being stacked in longitudinally-staggered relationship. An example of such apparatus is shown and claimed in the above-referred to application Ser. No. 07/623,265--Klappert and Houser.
While the apparatus disclosed in the Klappert and Houser application performs quite satisfactorily for making amorphous steel transformer cores of moderate diameters, e.g., up to about 22 inches, some problems have been encountered in using such apparatus for making cores of larger diameters. More specifically, when such apparatus is used for making cores of larger diameters, telescoping of the turns of the core becomes a difficult-to-manage problem. The term "telescoping" as used herein, denotes displacement or shifting, of the trailing edges of the stack in a lateral direction with respect to the leading edge during the wrapping-about-the-arbor operation. This telescoping action, as it applies to silicon-steel transformer core manufacturing, is described in greater detail in U.S. Pat. No. 4,476,632--Klappert, assigned to the assignee of the present invention. Telescoping can also be a problem in the manufacture of cores made from groups or packets of amorphous steel strip wrapped about an arbor.
An object of our invention is to provide simple and effective means for reducing the tendency of the groups or packets of amorphous metal strip to telescope as they are being wrapped about the arbor of a belt-nesting machine, especially in the case of the very long groups or packets that are wrapped about the arbor to form the outer turns of a large diameter core. To provide a better appreciation of this problem, it is noted that the outer packet of a 35 inch diameter core is about 124 inches long, and it is typically made up of several hundred thin strips of amorphous steel.
It is quite difficult to prevent such a long packet from telescoping and sustaining damage during transfer to the arbor and subsequent belt nesting. We are concerned with preventing the amorphous strip in packets of this type from being damaged by such telescoping.
Another object is to wrap the very thin amorphous metal strips in such a manner that there is a reduced tendency for the strips to develop undesirable wrinkles during wrapping and also a reduced tendency for air pockets to develop between the strips during wrapping.